In cylindrical wire slit filters it is known for the liquid to flow from the inside inwardly, or from the inside outwardly, and for the cylindrical filter basket or filter insert to be rotated manually or by a motor at regular intervals (or continuously), to strip off solids which have become deposited on the outer filter surface. The stripping device has a scraper which may fill up the gaps in the filter, thereby reducing its performance.
Nor are the suspended solids contained in the liquid to be filtered reliably enough conveyed downwards if vertically disposed brushes are substituted for a scraper.